Homing missile steering system

ABSTRACT

1. In an acoustic homing torpedo of pulse-echo type having means for converting received target echoes to output signals defining the sense of target direction referenced to torpedo heading, in combination, means controlled by said output signals for providing target direction samplings in the form of charge increments which are substantially uniform but of sign corresponding to the sense of target direction, means for decaying each of said samplings in accordance with a predetermined time-function to provide weighting which favors the most recent sampling, means for providing a continuous algebraic cumulation of the decaying samplings, means for providing a steering command signal having characteristics varying in accordance with the varying sign and magnitude of the said algebraic cumulation, and torpedo steering means controlled by the steering command signal and in accordance with said characteristics thereof to provide target homing action in which the sense and rate of torpedo turns correspond to the varying sign and magnitude, respectively, of said algebraic cumulation.

United States Patent [191 Altar et a1.

[4 1 Mar. 27, 1973 HOMING MISSILE STEERING SYSTEM EXEMPLARY CLAIM [75] Inventors: William Altar; Carl W. Helstrom, 1. In an acoustic homing torpedo of pulse-echo type Jr., both of Pittsburgh, Pa. having means for converting received target echoes to [731 W m Amen-w as fisszzssiirgfissiismtt czfnsrnziofi 'fsssz I fs by the Secretary of the controlled by said output signals for providing target direction samplings in the form of charge increments [22] Filed: Apr. 30, 1957 which are substantially uniform but of sign cor- A u N J 61 responding to the sense of target direction, means for PD 0 65 68 decaying each of said samplings in accordance with a predetermined time-function to provide weighting [52] US. Cl. ..ll4/23, 1 14/21, 340/6 whi h favors the most recent sampling, means for [51] Int. Cl ..F42b 19/01,G01v 1/00 viding a continuous algebraic cumulation of the 0 Search S, T, D; decaying arnplings means for a steering 3/ 7 command signal having characteristics varying in ac- 21 21 A, 5; 340/6, 6 R cordance with the varying sign and magnitude of the said algebraic cumulation, and torpedo steering means References Cited controlled by the steering command signal and in accordance with said characteristics thereof to provide UNITEDYSTATES PATENTS target homing action in which the sense and rate of 2,628,349 2/1953 Nightenhelser ..343/6 torpedo turns correspond to the varying sign and mag- 2,5l6,356 7/1950 Tull et a1. ....343/7 nitude, respectively, of said algebraic cumulation. 1,892,431 12/1932 Hammond, Jr ..l14/21 6 Claims, 2 Drawing Figures Primary Examiner-Benjamin A. Borchelt Assistant ExaminerJames M. l-lanley Attorney-V. C. Muller and Q.. B. Warner TRANSMITTER 10 u l3 l2 4" I n??? [j l TIMER L-' A 25 e5 67 ea 24 22 i9 11 16 RECEIVER i 49 J YQ ACTUATOR- l7 23 s9 62 Z J. I 21 I I I5 I 1. 47

l' 0- l i i PATENTEDHAR 27 I975 EDGE-O QEQKdIO muQODm mmzmomm mvErJfoRs W|LLIAM ALTAR CARL w. HELSTROM, JR. BY

ATTORNEYS HOMING MISSILE STEERING SYSTEM The present invention relates to torpedoes, and more particularly to a homing torpedo in which a memory and computer device operates upon samplings of target direction information in such manner as to provide more effective homing action.

The invention is of especial utility in an activeacoustic-homing torpedo employing a pulse-echo principle of target detection and location, a type of torpedo here briefly described in order to present exemplary environment of the invention, and to provide understanding of shortcomings in the pertinent prior art and recognition of the improvement afforded by the present invention. Such a torpedo is often designed to first run a predetermined time or distance toward a suspect region, to then switch to a target search phase in which the torpedo steering equipment is controlled in accordance with some predetermined plan to effect a sweeping search of the suspect region and upon target detection to then effect switch-over to circuitry suitable for the target pursuit phase in which the torpedo attempts to continuously home toward the target. Upon switching to the target search phase, the torpedo repeatedly pings, that is, generates and projects bursts of ultrasonic energy. When a target is found within the torpedos detection pattern and close enough to provide an echo of suitable magnitude, the torpedo utilizes the target echo in a manner to effect target acquisition, that is, to switch torpedo operation to the pursuit phase. Upon target acquisition and during the pursuit phase, target direction information is derived from the target echoes, thus effectively in the form of samplings. So long as target direction samplings continue to be available, the torpedo is repetitively commanded to turn toward the target, but at a fixed turn rate. The torpedo thus attempts to continuously point toward the target within relatively small angular limits, or at least to bracket the target within confines of the torpedos detection pattern so that target echoes and target direction information will not be lost.

. In the prior'torpedo art, then, the fixed turn rate and the isolated piecemeal manner in which the successive samples of target direction information are utilized imposes certain' restrictions and disadvantages. Target loss must inevitably occur in certain situations where target speed and geometry of the attack are such that the compromise rate of turn cannot hold the target within bounds of the effective detection field of the torpedo. Certain torpedoes will in fact at times lose the target even though it is well within the detection field. In particular, one such type of torpedo effects target recognition and acquisition by utilization of target- Doppler shift, a frequency shift in the ultrasonic carrier of the target echo, which frequency shift occurs when the target is in motion and presents either an opening or closing velocity component along the torpedo heading. Such a torpedo therefore suffers a blind condition when its target is at or near 90 aspect, essentially broadside to the torpedo, wherein it fails to provide a target-Doppler shift exceeding a practical threshold value, resulting in effective target loss despite the fact that the target is then actually within the torpedos detection field. The information carried by each target direction sample, generally limited to only the sense of target direction, is utilized only during that ping cycle in which it is received, and is thereafter discarded in favor of the next sample. When for any reason the next target direction sample or the next several samples are not received, steering information is then not available, and this condition generally leads to continuing target loss, reversion to the search phase, and deterioration of the overall target kill probability.

It is a primary object of the present invention to provide an improved homing torpedo wherein target direction information is sampled, stored and operated upon to yield steering control signals which provide essentially optimum torpedo homing action.

It is another object to provide an improved homing torpedo system wherein memory and computer functions combine to effectively provide information as to probable sense and magnitude of target direction relative to torpedo heading.

It is another object to provide an acoustic homing torpedo which repetitively samples target direction information and operates upon the samplings to derive therefrom steering control signals which provide varying rates of torpedo turn essentially as required for optimum homing action of the torpedo during its target pursuit phase.

It is a further object to provide an improved homing torpedo wherein target direction information is sampled, stored and operated upon to yield steering control signals which provide continuity of torpedo homing action during temporary loss of target direction samplings.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of an exemplary embodiment considered in conjunction with the accompanying drawing wherein:

FIG. 1 illustrates pursuit phase circuitry of an activeacoustic-homing torpedo system employing relay-controlled switching means for application of target direction samplings to a memory device;

FIG. 2 illustrates a modified form of memory device and input circuitry control means therefor. The present invention is concerned with improvements in homing action in the pursuit phase of torpedo operation, and will be described with particular reference to steering control in azimuth alone, since this simplifies the presentation and suffices for an understanding of the invention. While in some instances target pursuit may also require corrective homing action in depth, as in anti-submarine operation, steering in an azimuth plane is always more demanding than steering in depth because of greater maneuverability of targets in the azimuth plane. Control of steering in depth is in general easily satisfied by conventional techniques. However, principles of the invention are of course to be understood as also applicable to provide improved homing action in depth where this may appear desirable.

It has been found that in principle an optimum course of torpedo pursuit action, as to the probable rates of turn that should be provided at successive instants, can be determined from past samplings of target direction information even when these samplings provide only sense of target direction. In accordance with the present invention, there is provided a system including a memory device which in effect stores the successive samples of target-bearing information, assigns a suitable timeedecay factor to each sample, forms a cumulative function of these time-decaying samples, and provides steering control signals corresponding to the resultant function. The time-decay factor in effect progressively weights the samples to favor the more present ones over the earlier ones, so that the most recent sample has greatest importance, and so that all samples which arrived more than several ping cycles earlier are essentially ineffective. In particular, an exponential decay with time has been found to provide near-optimum results in a sampling memory system of this type, and the embodiment here described provides such a decay function in a very simple yet effective manner.

FIG. 1 illustrates this simplified yet effective memory system in combination with exemplary active-acoustichoming torpedo circuitry, in accordance with the present invention. Conventional and well understood units are shown largely in block diagram form. The torpedo is of course to be understood as being under way, and operating in pursuit against a target. By way of example, this torpedo may be of pulse-echo type employing a pinger relay which is periodically closed by conventional timing switch means 11 to key transmitter 12, via switch 13 of relay 10, for transmission periods of say 40 milliseconds or less duration, and at intervals of say 1.25 seconds. Transmitter 12 provides a transducer-energizing voltage of suitable ultrasonic frequency at output lead 14 during the brief transmission periods. Transmission of ultrasonic pings and reception of the resultant ultrasonic target echoes may be accomplished by means of a single electro-acoustic transducer 15 having side-by-side magnetostrictive sections 16 and 17 in accordance with known practice, and this transducer is to be understood as centrally located in the torpedo nose. The transducer sections 16 and 17, transmitter 12, receiver 18, and the switch elements of pinger relay 10, are arranged and connected as shown so that the transducer sections 16 and 17 are energized in parallel during transmission, but during reception are individually connected to separate receiver channels through leads 19 and 20. Ground symbols are applied to the voltage reference or circuit return leads of transmitter 12, transducer 15 and receiver 18, which are connected in common and which may in fact be grounded to the torpedo frame. In accordance with conventional usage and as well understood, the provision of side-by-side transducer sections and their separate operation during reception periods yields, for each target echo, a pair of electrical target echo signals having relative phase characteristics which identify target location. Upon reception of a target echo resulting from transmission of a pulse of ultrasonic energy by transducer 15, transducer sections 16 and 17 each deliver a target echo signal to receiver channels 19 and 20, respectively, these dual signals at ultrasonic frequency being essentially of like amplitude but exhibiting a phase difference substantially corresponding to bearing deviation of the target relative to the torpedo heading at the instant of echo reception. Receiver 18 is of any conventional type suitable for conversion of these phase-differing target echo signals to target direction signals which identify the sense of target bearing, generally in the form of direct voltages which can conveniently be utilized for control of one or more relays or other switching devices. In this instance, for use in controlling a difierential relay 21 having separate windings 22 and 23, receiver 18 supplies the target direction signals in the form of unipolar voltage pulses to distinct output channels, represented by the separate output leads 24 and 25, circuit return being made via lead 26. For each received target echo, a voltage pulse is provided at one or the other of output leads 24 and 25, depending upon the sense of target bearing deviation as determined from the target echo signals. These voltage pulses may be of either like or unlike polarity, for this is simply a matter of receiver circuitry design and the differential relay windings 22 and 23 can be connected to operate under either condition. Relay 21 preferably but not essentially is designed in accordance with conventional techniques to close swinger arms 27 and 28 against their upper or lower contacts (as the case may be, dependent upon delivery of a voltage pulse to upper or lower relay coil 22 or 23) just before swinger arm 29 is closed against its upper or lower contact. This is desirable in order that the parallel RC (resistor/capacitor) type of memory device 30 shall first be placed in circuit, so that charging circuit 40 may deliver to capacitor 41 an amount of charge which is predetermined exactly under time control of gate circuit 42. The gate circuit may be of any conventional type, for example a one-shot or univibrator circuit of the heavily biased relaxation type, adapted when suitably triggered to supply, at output lead 43 relative to circuit return lead 44, a gate pulse of positive polarity, and of predetermined magnitude and duration. Gate circuit 42 is here triggered by application of voltage from source 45 upon input circuit completion through operation of swinger arm 29 against either of its adjacent contacts. Charging circuit 40 operates, during application thereto of the positive gate pulse, to deliver a charging current of essentially constant value to capacitor 41 via output leads 46, 47. Charging circuit 40 in this instance comprises simply a triode amplifier including a current limiting resistor 48 as shown, normally biased to a cut-off condition but rendered conductive during application of the gate pulse. A pentode circuit or any other suitable constant current generator may be utilized instead. Gate circuit 42 is arranged to provide a gate pulse of duration shorter than the period during which relay 21 remains operated, so that the charge delivered by charging circuit 40 is in fact controlled by the gate pulse and not cut off by opening of relay 21, which takes place before transmission of the next ping Further, the particular values of gate pulse duration, of the resistor and capacitor elements of memory circuit 30, the effective series resistance of charging circuit 40 and the magnitude of charging current delivered thereby, are so selected that the voltage across capacitor 41 does not build up to such relatively large magnitude as to deteriorate the desired constant current characteristic of charging circuit 40, and this is of course simply a matter of engineering design. In response to each received echo, therefore, charging circuit 40 thus delivers a fixed amount of charge to capacitor 41, producing a correspondingly fixed change in voltage thereacross, of positive or negative polarity in effect dependent upon the sense of target bearing deviation because of the corresponding reversing action of the target direction signals upon relay 21. Resistor 49 shunting capacitor 41 effects a charge bleeding action which attenuates or decays each positive or negative voltage increment supplied to capacitor 41, the RC combination inherently functioning to effect this decay exponentially with time and being designed to provide a decay time longer than one ping cycle but short enough to substantially extinguish those samples arriving more than a preselected number of ping cycles earlier. The voltage appearing across capacitor 41 at any instant corresponds to an algebraic cumulation of several preceding target bearing deviation samplings, which are each positive or negative in accordance with the sense of the deviations, and which are each decayed exponentially with time. The resultant capacitor voltage at any instant thus defines not only the sense but the probable magnitude of the target bearing deviation at that instant. This resultant voltage is utilized as an input command signal to a servo system which controls the torpedo steering and rate of turn, which servo system may be entirely conventional per se as illustrated.

In this servo system arm 60 of potentiometer 61 is linked to torpedo rudder 62, as indicated, and employed in a circuit arrangement 63 which provides a voltage corresponding in polarity and magnitude to the sense and magnitude of the rudder deflection, thus substantially corresponding to the sense and magnitude of the torpedo turn rate. This relationship can of course be made more accurate, if desired, by use of a rate gyroscope system in well known manner but at the expense of more elaborate equipment. The potentiometer circuit 63 is designed to provide, at lead 64, a bucking voltage substantially equal to the capacitor voltage at lead 65, relative to their common reference lead 66, when rudder 62is deflectEd through a suitable angle (to port or to starboard as the case may be) to provide the desired rate of turn in response to that capacitor voltage. The net voltage applied to servo-amplifier 67 is in effect an error voltage, utilized to control actuator 68 in such manner as to drive rudder 62 to an angular deflection which reduces the error voltage to zero. The rudder deflection thus follows the command voltage delivered by capacitor 41 and correspondingly produces a turn rate essentially proportional to the command voltage, and in the direction called for by the command voltage.

In this manner, then, the torpedo system including in combination therewith a memory device and switching circuitry as described becomes effective to eliminate the need for a compromise turn rate, to provide improved homing action both in normal pursuit situations and under adverse tactical situations which can be expected to be encountered in actual practice, and to provide holdover of steering information during transitory periods of target loss. On an essentially straight pursuit course, the torpedo can now home toward the target with but small angular deviations from a line-ofsight to the target, accomplishing its turns at a moderate rate and thus avoiding large overshoots. In a pursuit phase where the aspect angle of the target increases rapidly, the torpedo turn rate now increases to an extent which enables overtaking the target in angle and bracketing it to thus still obtain suitable sequences of target direction samplings. It is of course to be understood that the described system becomes most effective when the torpedo response time relative to the sampling interval is fast, and the sampling interval shorter than the time in which significant change in the tactical situation may take place.

FIG. 2 illustrates a modified memory circuit configuration Qfl, and a suitable relay switch arrangement therefor, which can be substituted for that shown in FIG. 1. In this instance, instead of applying both positive and negative increments to a single capacitor, charge increments of fixed sign are applied to one or the other of a pair of series-connected capacitors 91, 92 in accordance with the sense of target bearing deviation as determined by'the signal receiving equipment. This is accomplished through switch 93 of differential relay 94, actuated in accordance with energization of the relay windings as described in connection with the embodiment shown in FIG. 1. Differential relay 94 may be entirely similar to relay 2] except for absence or non-use of one of the switch units shown in relay 21. Again, the series-connected capacitors 91, 92 are shunted by a bleeder resistor 95, and the voltage across resistor 95, experiencing exponential decay as before, corresponds to an algebraic cumulation of target bearing deviation samplings and may be utilized for improved homing control in a manner already described.

Various modifications of the above-disclosed apparatus will occur to those skilled in the art. For example, it may appear desirable in some applications of the invention to avoid use of an electromagnetic type of switching device. In such event the described embodiments may be modified to employ strictly electronic switching means, using tubes or transistor arrangements, and any conventional type of gate circuit adapted to provide a delayed gate pulse when energized or triggered, in accordance with now well known techniques and still under control and triggering action of voltage pulses delivered by the receiver as disclosed.

Obviously other modifications and variations of the present invention are thus possible in the light of the above teachings. It is therefore to be understood that within'the scope of the appended claims the invention may be practiced otherwise than as specifically described.

. What is claimed is:

1. In an acoustic homing torpedo of pulse-echo type having means for converting received target echoes to output signals defining the sense of target direction referenced to torpedo heading, in combination, means controlled by said output signals for providing target direction samplings in the form of charge increments which are substantially uniform but of sign corresponding to the sense of target direction, means for decaying each of said samplings in accordance with a predetermined time-function to provide weighting which favors the most recent sampling, means for providing a continuous algebraic cumulation of the decaying samplings, means for providing a steering command signal having characteristics varying in accordance with the varying sign and magnitude of the said algebraic cumulation, and torpedo steering means controlled by the steering command signal and in accordance with said characteristics thereof to provide target homing action in which the sense and rate of torpedo turns correspond to the varying sign and magnitude, respectively, of said algebraic cumulation.

2. An acoustic homing torpedo combination as defined in claim 1, wherein said predetermined timefunction provides an exponential decay.

3. An acoustic homing torpedo combination as defined in claim 1, wherein said means for providing target direction samplings comprises a gate circuit triggered by said output signals to provide a gate pulse of predetermined duration, and a constant current generator controlled by said gate pulse to supply a predetermined charge increment.

4. In an acoustic homing torpedo of pulse-echo type having means for converting received target echoes to output signals defining the sense of target direction referenced to torpedo heading, in combination, a memory circuit comprising capacitive and bleeder resistance elements, means controlled by said output signals for applying to said memory circuit target direction samplings in the form of charge increments which are substantially uniform but of sign corresponding to the sense of target direction, said memory circuit decaying each of said samplings exponentially and providing a continuous algebraic cumulation of the decaying samplings, means for providing a steering command signal having characteristics varying in accordance with the varying sign and magnitude of the said algebraic cumulation, and torpedo steering means controlled by the steering command signal and in accordance with said characteristics thereof to provide target homing action in which the sense and rate of torpedo turns correspond to the varying sign and magnitude, respectively, of said algebraic cumulation.

5. An acoustic homing torpedo combination as defined in claim 4, wherein said means for providing target direction samplings comprises a gate circuit triggered by said output signals to provide a gate pulse of predetermined duration, and a constant current generator controlled by said gate pulse to supply a predetermined charge increment.

6. In a missile homing system, means for deriving target direction samplings having sign characteristics corresponding to the sense of target direction, means for decaying each of said samplings in accordance with a predetermined function to provide weighting which favors the most recent sampling, means for providing a continuous algebraic cumulation of the decaying samplings, and control signal means for providing missile turns of sense and rate in accordance with the sign and magnitude of said continuous algebraic cumulation of the decaying samplings. 

1. In an acoustic homing torpedo of pulse-echo type having means for converting received target echoes to output signals defining the sense of target direction referenced to torpedo heading, in combination, means controlled by said output signals for providing target direction samplings in the form of charge increments which are substantially uniform but of sign corresponding to the sense of target direction, means for decaying each of said samplings in accordance with a predetermined time-function to provide weighting which favors the most recent sampling, means for providing a continuous algebraic cumulation of the decaying samplings, means for providing a steering command signal having characteristics varying in accordance with the varying sign and magnitude of the said algebraic cumulation, and torpedo steering means controlled by the steering command signal and in accordance with said characteristics thereof to provide target homing action in which the sense and rate of torpedo turns correspond to the varying sign and magnitude, respectively, of said algebraic cumulation.
 2. An acoustic homing torpedo combination as defined in claim 1, wherein said predetermined time-function provides an exponential decay.
 3. An acoustic homing torpedo combination as defined in claim 1, wherein said means for providing target direction samplings comprises a gate circuit triggered by said output signals to provide a gate pulse of predetermined duration, and a constant current generator controlled by said gate pulse to supply a predetermined charge increment.
 4. In an acoustic homing torpedo of pulse-echo type having means for converting received target echoes to output signals defining the sense of target direction referenced to torpedo heading, in combination, a memory circuit comprising capacitive and bleeder resistance elements, means controlled by said output signals for applying to said memory circuit target direction samplings in the form of charge increments which are substantially uniform but of sign corresponding to the sense of target direction, said memory circuit decaying each of said samplings exponentially and providing a continuous algebraic cumulation of the decaying samplings, means for providing a steering command signal having characteristics varying in accordance with the varying sign and magnitude of the said algebraic cumulation, and torpedo steering means controlled by the steering command signal and in accordance with said characteristics thereof to provide target homing action in which the sense and rate of torpedo turns correspond to the varying sign and magnitude, respectively, of said algebraic cumulation.
 5. An acoustic homing torpedo combination as defined in claim 4, wherein said means for providing target direction samplings comprises a gate circuit triggered by said output signals to provide a gate pulse of predetermined duration, and a constant current generator controlled by said gate pulse to supply a predetermined charge increment.
 6. In a missile homing system, means for deriving target direction samplings having sign characteristics corresponding to the sense of target direction, means for decaying each of said samplings in accordance with a predetermined function to provide weighting which favors the most recent sampling, means for providing a continuous algebraic cumulation of the decaying samplings, and control signal means for providing missile turns of sense and rate in accordance with the sign and magnitude of said continuous algebraic cumulation of the decaying samplings. 